Introduction

Municipal wastewater treatment plants (WWTPs) face a dual challenge: they must meet increasingly strict discharge permits while handling rising volumes of domestic, commercial, and industrial sewage. Traditional secondary treatment using activated sludge removes most biodegradable organics, but it often falls short on color removal, odor control, and the elimination of recalcitrant pollutants. This is where ozone treatment has emerged as a powerful tertiary and advanced oxidation solution.

At Tonglin Ozone, we supply industrial-grade ozone generators engineered for continuous municipal-duty operation. This guide explains how ozone improves effluent quality, compares it with conventional disinfection technologies, and outlines practical design considerations for engineers and plant operators.

Why Municipalities Are Turning to Ozone

Global discharge standards are tightening. Parameters such as chemical oxygen demand (COD), biochemical oxygen demand (BOD), total suspended solids (TSS), and fecal coliform counts are no longer the only concerns. Regulators now also monitor residual pharmaceuticals, personal care products, endocrine-disrupting compounds, and nutrient levels. Ozone addresses these challenges through rapid, non-selective oxidation.

• Powerful oxidation potential — Ozone is one of the strongest commercially available oxidants, second only to fluorine.
• No harmful chlorinated byproducts — Unlike chlorine, ozone does not form trihalomethanes (THMs) or haloacetic acids.
• Short contact time — Effective disinfection is typically achieved in 5–15 minutes.
• Oxygen-only residual — Ozone decomposes to oxygen, leaving no chemical residue in the final effluent.
• Odor and color reduction — Breaks down chromophores and sulfurous compounds responsible for unpleasant smells.

Key Applications in Municipal Wastewater Plants

Tertiary Disinfection

After biological treatment and clarification, municipal effluent still contains pathogens. Ozone is installed as a tertiary barrier to inactivate bacteria, viruses, and protozoan cysts before discharge to surface water or reuse applications. Typical dosages range from 5 to 15 mg/L depending on effluent quality and target log reduction.

COD and BOD Polishing

For plants needing to meet low COD limits or preparing water for industrial reuse, ozone oxidizes residual organics that microorganisms cannot degrade. When combined with hydrogen peroxide or UV in an advanced oxidation process (AOP), removal efficiency can increase significantly.

Color and Odor Removal

Industrial contributions to municipal sewers often introduce dyes, lignins, and sulfides that persist through biological treatment. Ozone bleaches color bodies and neutralizes odorous compounds such as hydrogen sulfide and mercaptans, improving community acceptance and reducing nuisance complaints.

Micropollutant and Pharmaceutical Degradation

Trace contaminants including antibiotics, hormones, and microplastics are difficult to remove biologically. Ozone attacks these compounds through direct molecular oxidation and indirect hydroxyl radical reactions, helping municipalities future-proof their plants against emerging regulations.

Ozone vs. Traditional Disinfection Methods

Design and Sizing Considerations

A successful ozone system for municipal wastewater requires more than selecting an ozone generator. Engineers must evaluate flow rate, water quality, ozone transfer efficiency, and contactor design.

• Ozone dose: Typically 5–20 mg/L for tertiary disinfection; higher for COD or color removal.
• Transfer system: Venturi injection or fine-bubble diffusers maximize mass transfer.
• Contact tank: Provides retention time and plug-flow conditions; usually concrete or stainless steel.
• Destruction unit: Converts off-gas ozone back to oxygen before venting.
• Oxygen source: PSA oxygen concentrators or liquid oxygen (LOX) feed higher-concentration ozone generators.

For a plant treating 5,000 m³/day with an ozone dose of 10 mg/L, the required ozone production capacity is approximately 2.1 kg O₃/h when accounting for 90% mass transfer efficiency.

Implementation Best Practices

• Pre-treat upstream: Remove suspended solids and reduce COD biologically before ozone to minimize ozone demand.
• Monitor ORP and residual ozone: Online oxidation-reduction potential (ORP) sensors help optimize dosing in real time.
• Plan for redundancy: Install multiple ozone generators or backup oxygen supply to avoid process interruptions.
• Ensure safety compliance: Use ambient ozone detectors, emergency ventilation, and certified electrical panels.
• Train operators: Ozone systems are safe and reliable when operated by trained personnel following SOPs.

Conclusion

Ozone offers municipalities and wastewater contractors a versatile, chemical-free solution for tertiary disinfection, COD polishing, color removal, and micropollutant control. With proper system design and oxygen feed, ozone generators can help treatment plants meet current discharge limits and prepare for tomorrow's water reuse opportunities.

Whether you are designing a new WWTP or retrofitting an existing facility, Tonglin Ozone provides reliable ozone generation systems backed by technical support and export experience.